1. What is the Duct Size Equation?

The duct size equation calculates the required cross-sectional area of a duct based on airflow rate and velocity. It's fundamental in HVAC system design to ensure proper air distribution while minimizing energy losses.

2. How Does the Calculator Work?

The calculator uses the duct size equation:

Where:

• \( A \) — Duct cross-sectional area (square feet)
• \( CFM \) — Airflow rate (cubic feet per minute)
• \( V \) — Air velocity (feet per minute)

Explanation: The equation balances airflow requirements with velocity constraints to determine appropriate duct dimensions.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing is crucial for efficient HVAC operation. Undersized ducts increase resistance and energy consumption, while oversized ducts are costly and may lead to poor air distribution.

4. Using the Calculator

Tips: Enter CFM (typically 300-900 for residential systems) and desired velocity (typically 600-900 fpm for main ducts). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical velocity ranges for different duct types?
A: Main ducts: 600-900 fpm, branch ducts: 600-700 fpm, final runs: 400-600 fpm.

Q2: How does this relate to round duct sizing?
A: For round ducts, convert area to diameter using \( D = 2 \times \sqrt{A/\pi} \).

Q3: What factors affect velocity selection?
A: Noise considerations, space constraints, energy efficiency, and system static pressure.

Q4: Are there standard duct sizes?
A: Yes, ducts typically come in standard sizes (4", 6", 8", etc.), so you'll round up to the nearest available size.

Q5: How does duct material affect sizing?
A: Material affects friction loss but not the basic area calculation. Different materials may require adjustments for equivalent performance.